Using TRNSYS as the software chosen for the simulations, it was possible to achieve the intended objectives. The simulation in this program and in all others that simulate HVAC installations, require a lot of attention and technical data, not only of the building parameters, but also of the climate, the desired temperature profile, and the technical details of the
equipment. Before introducing the components in the simulation mode, it is always necessary to make a pre-dimensioning to be able to get closer to the objective. When the equipment has been chosen, we introduce it as external files in the simulation, as there is many equipment that is not in the TRNSYS bookstore, so that it is possible to simulate the chosen component with greater precision (normalized data).
As it is a very old building, and it was not possible to obtain exact details about its entire structure, many assumptions have been made. Therefore, the results obtained can vary a lot depending on its user. The many considerations that have been made in this project, turns this work more subjective and therefore they need to be explained accordingly as the project progresses.
The study tried to understand to what extent it would be feasible to replace a gas boiler with a geothermal heat pump, and for that it was necessary to simulate both systems. For a more complete study, several hypotheses were studied in addition to the current system. Not only was a photovoltaic system analysed, but also something very important that people usually forget when it comes to saving the planet, namely insulation. This is a parameter perhaps as important as the replacement of the energy source itself, because as we saw in the results presented in the previous section, it is possible to save both in annual costs and in expelled emissions. The thermal insulation means that the gas boiler can be dimensioned 20 kW below the current level and an additional 3000 € per year as well as 6 tonnes of CO2 can be saved.
The first big challenge was choosing an appropriate heat pump, since the necessary condition was that the GSHP needed to reach temperatures of 75 ºC. This condition was not easy to overcome, because even managing to get a high heat power, most of the pumps found on the market only guaranteed maximum temperatures around 60 ºC. This would represent a great loss of energy compared to the existing gas boiler. As the heat pump would be connected to the radiators, and if we wanted to maintain the same heat performance, we would have to guarantee the same outlet temperature. Since this temperature is quite high for the use of heat pumps, very low performance values (COP) have been obtained compared to other
applications. To take advantage of the full potential of these devices, the heat pump must be connected to medium temperature emitters between 40-60 ºC (like underfloor radiating), as it is in this range that the COP values are higher.
The study revealed that it is possible to retrofit an old building with heat pumps using the current hot water distribution system, without major problems. Since the building requires high thermal loads, all equipment must be oversized. This over-dimensioning is desirable, as it manages to have a greater margin of manoeuvre if necessary. It is important to consider that if we want to have a good performance/cost ratio, we need a large initial investment
especially in large and old buildings.
Although it is not possible to use underfloor heating in the church, as well as insulation, this would be by far the best possible solution for our case study. It is also important to point out that the photovoltaic system brings an added value to the system, as it manages to produce 10 645 kWh of energy converted into AC. This translates into an annual saving of 2660€ which, in conjunction with the heat pump, leads to a saving of 8 tonnes of CO2 a year. Finally, the best solution, although impractical in this case, could save 22 tonnes of CO2 and 7000€ per year. In an ecological and realistic analysis, replacing a boiler with a heat pump is, despite the
high investment, feasible, even with 70 years of ROI. Being a protected building that will exist for many more years, that time will eventually come, and till then it will save many tons of CO2. An alternative would be to get an agreement with the Irish government and be able to add thermal insulators without damaging/changing the building, for example on the inner side of the roof. A small change in legislation could help a lot in fighting climate change.
It is difficult for personal homes or even in public buildings, to start changing the way we heat our spaces. In fact, natural gas is much cheaper than electricity in Ireland and boilers can achieve yields of up to 90% not requiring a large investment. It is understandable that not everyone has the possibility to invest in renewable energies, however there are other
alternatives that can be equally advantageous for saving energy, reducing bills and emissions.
There are more and more incentives on the part of governments to call on people to be part of this much needed change, which is a great indicator and gives us hope for a cleaner and more sustainable world.
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APPENDIX A – Building model in Google Sketchup
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APPENDIX B – Gas boiler LOGANO G315
APPENDIX C – BURNER RIELLO GS10
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APPENDIX D – RADIATOR FROM MaxHeat
APPENDIX E – HEAT PUMP UNIT
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